There are many fields of manufacture in which the interior of a base body, such as a pipe or tube, or a segment thereof, is metalized over an ordinary metal such as steel with an expensive surface layer treatment or coating that is fused to the base metal in order to provide a finished product that will respond to manufacturing specifications, but which is less expensive than making the entire body of the same material that the coating specifications require. Thus, parts such as the interior of pipes or tubes used to convey corrosive or abrasive fluids, liquids, slurries and the like, are frequently required to provide thereon an interior metalized surface of chromium, or chrome, or other special metal or metal alloy, that will either resist corrosion and wear or will provide a good bearing surface. In strings of pipe used in deep oil wells, for example, it is desirable that the interior surface of the pipe have resistance to corrosion and wear, so as to extend the time period during which a string of pipe will function before corrosion or abrasive failure causes disruption of oil production and consequent increase of costs. Similarly, strings of pipe which are used to transport concrete slurry from a source of supply to the site of use, must have a wear resistant inner surface in order to withstand the abrasion of the inner surface which is caused by the aggregate (sand, gravel, and crushed stone) which is mixed with the cement in the concrete slurry.
It has been long known that ordinary steels, except for leaded steels or resulphurized steels, may be chrome surfaced by plating or the like, to meet the specifications for desired strength of the part and provide the surface character specially required for exposure to a harsh environment in which the part is to be used.
However, chromium, for example, is a relatively expensive material, and the use of chromium in various chemical baths by which chrome plating may be effected, is environmentally undesirable, operationally difficult and expensive to control. Also, it is technically difficult to deposit a metalizing layer of any substantial thickness onto the interior surface of tubes or pipes, or segments thereof, that are to serve as the bearing surface of a bearing or journal element. Moreover, the deposition of thin layers of coating metals upon the inside surface of pipes and tubes has been extremely difficult when the pipe or tube has a small diameter, such as for nominal pipe sizes of about three inches or less.
In order to avoid such potential problems, a coating apparatus has been recently fabricated and operated which comprises a plurality of first rotatable rollers mounted on a first rotatable shaft having an inlet end and an outlet end, and a plurality of second rotatable rollers mounted on a second rotatable shaft having an inlet end adjacent the inlet end of the first rotatable shaft, and having an outlet end adjacent the outlet end of the first rotatable shaft. Each second roller is spaced from and adjacent to a corresponding first roller in a paired relationship to thereby define a gap of fixed dimension between each pair of adjacent first and second rollers.
A heating means which is operable to melt and fuse a powdered metal coating to the inside surface of a rotating pipe is located proximate the outlet ends of the first and second shafts.
A plurality of third rollers mounted on a third rotatable shaft having an inlet end proximate the heating apparatus and having an outlet end spaced from the heating apparatus is paired on the discharge side of the heating apparatus with a plurality of fourth rollers mounted on a fourth rotatable shaft having an inlet end adjacent the inlet end of the third rotatable shaft, and having an outlet end adjacent the outlet end of the third rotatable shaft. Each fourth roller is spaced from and adjacent to a corresponding third roller in a paired relationship to thereby define a gap of the fixed dimension between each pair of adjacent third and fourth rollers.
A nesting groove is located above the gap between each pair of rotatable rollers and between the adjacent portion of the upper surfaces of each pair of rotatable rollers. This nesting groove provides horizontal support for an elongated tubular body, such as a pipe or tube, which is to be internally coated with metal.
A first motive means is utilized for rotating the first and second rotatable shafts and the mounted first and second rollers to thereby rotate the elongated tubular body within the nesting grooves of adjacent pairs of first and second rollers, and a second motive means is utilized for rotating the third and fourth rotatable shafts and the mounted third and fourth rollers to thereby rotate the elongated tubular body within the nesting grooves of the adjacent pairs of the third and fourth rollers.
A separate individual axial advancing means is used for longitudinally advancing the rotating elongated tubular body sequentially along the nesting grooves between adjacent pairs of first and second rollers, through the heating means, and sequentially along the nesting grooves between adjacent pairs of third and fourth rollers. Finally, the means for internally coating the elongated tubular body is a spray head which is located within the heating element for depositing the particulate coating material on the inside surface of the pipe.
While this novel apparatus has been successful in eliminating many of the problems which may have been encountered by use of the prior art techniques, a new and different problem has been encountered with the novel apparatus. It has been found that as the heated rotating pipe is discharged from the heating means, there is an occasional problem which arises due to vibration of the hot pipe advancing along the sequence of nesting grooves between the third and fourth rollers on the discharge side of the heating unit. This vibration occasionally becomes so intense that the rotating hot pipe may eventually vibrate sufficiently to fly off of the array of third and fourth rollers and onto the floor. Occasionally, the vibrating pipe may touch the induction heating coil which is located within the heating means and short-out the heater, thereby causing premature shutdown of the entire operating unit.
Accordingly, it is an object of the present invention to provide a method and apparatus for internally coating a metal tube or pipe without encountering excessive vibration of the tube or pipe as it is withdrawn from the heating apparatus and cooled while rotating and longitudinally advancing along the sequence of nesting grooves between the adjacent pairs of third and fourth rollers in the coating apparatus.
It is another object of the present invention to provide a method and apparatus for internally coating a metal pipe or tube without encountering vibration of the tube or pipe as it is withdrawn from the heating apparatus which is sufficient to cause the tube or pipe to be thrown out of the nesting grooves between the pairs of third and fourth rollers and onto the floor of the plant.
It is a further object of the present invention to provide a method and apparatus for internally coating a metal tube or pipe without vibration which is sufficient to cause the rotating and longitudinally advancing metal tube or pipe to touch the electrical elements of the heating unit and thereby cause a short circuit which shuts down the entire coating system.
These and other objects of the present invention, as well as the advantages thereof, will become more clear to those skilled in the art from the disclosure which follows.